CBSE Class 10 Biology How do Organisms Reproduce MCQs Set 11

Answer: (b) seed

Explanation:
1. After fertilisation the ovule becomes the seed and the ovary becomes the fruit.
2. The seed contains the embryo and its stored food.

Teacher's Note:
1. Ovule → seed and ovary → fruit.
2. Do not mix them up.

Answer: (c) fertilisation

Explanation:
1. Fertilisation mixes the genes of two parents, producing variations.
2. Accumulation of variations over generations can give rise to new species, unlike the clone-forming methods.

Teacher's Note:
1. Variation is the raw material of evolution.
2. Asexual methods give little variation.

Answer: (b) male and female gametes

Explanation:
1. A zygote is the cell formed when a male gamete fuses with a female gamete.
2. Spores take part in asexual reproduction only.

Teacher's Note:
1. Fertilisation = fusion of gametes.
2. The zygote grows into the embryo.

Answer: (d) P, Q, R and S

Explanation:
1. Planaria has specialised cells all over its body that can multiply and form the missing parts.
2. So every piece, P, Q, R and S, regenerates into a complete worm.

Teacher's Note:
1. Regeneration works on any piece of Planaria.
2. It is not limited to the head.

Answer: (d) Bryophyllum

Explanation:
1. Bryophyllum has buds in the notches of its leaves that fall and grow into new plants.
2. Potato forms new plants from its stem tubers.

Teacher's Note:
1. Leaf buds are typical of Bryophyllum.
2. Potato uses stem 'eyes'.

Answer: (c) grafting

Explanation:
1. In grafting the root system of one plant is joined to the shoot of another plant.
2. The new plant thus has the desirable characters of both.

Teacher's Note:
1. Layering and cutting give copies of one plant.
2. Grafting joins two different plants.

Answer: (d) Rose - root

Explanation:
1. Bryophyllum reproduces through leaf buds, potato through its tubers (stems) and money plant through stem cuttings.
2. Rose is propagated by stem cuttings, not roots, so the match is wrong.

Teacher's Note:
1. Learn plant-part examples in pairs.
2. Sweet potato and dahlia are root examples.

Answer: (c) root

Explanation:
1. Sweet potato has fleshy tuberous roots that carry adventitious buds.
2. When these roots are planted in soil, the buds grow into new plants, so propagation is by the root.

Teacher's Note:
1. Learn the standard examples: roots (sweet potato, dahlia), stems (potato, ginger), leaves (Bryophyllum).
2. This is a common one-mark question.

Answer: (d) either stamen or carpel

Explanation:
1. A unisexual flower has either stamens or carpels, never both.
2. Papaya and watermelon are examples.

Teacher's Note:
1. Bisexual flowers have both stamens and carpels.
2. Unisexual = one sex only.

Answer: (c) stamen

Explanation:
1. The stamen, made of anther and filament, produces pollen grains with male gametes.
2. The pistil or carpel is the female part.

Teacher's Note:
1. Stamen = male; carpel = female.
2. Sepals protect the bud.

Answer: (c) plumule develops into the root system

Explanation:
1. The plumule is the part of the embryo that grows into the shoot.
2. The radicle develops into the root system, so the third statement is incorrect.

Teacher's Note:
1. Plumule = shoot; radicle = root.
2. Seed coat protects the embryo.

Answer: (d) pistil and stamen

Explanation:
1. The essential, reproductive parts of a flower are the male stamen and the female pistil (carpel).
2. Sepals and petals are only accessory parts.

Teacher's Note:
1. Stamen and carpel produce the gametes.
2. Sepals protect and petals attract insects.

Answer: (b) A: ovary, B: stigma, C: style

Explanation:
1. The swollen basal part of the carpel is the ovary, where the ovules with female gametes are formed.
2. The sticky top is the stigma and the middle stalk joining them is the style.

Teacher's Note:
1. Carpel = stigma + style + ovary, from top to bottom.
2. Stigma receives pollen.

Answer: (a) testis → vas deferens → urethra

Explanation:
1. Sperms made in the testis pass through the vas deferens.
2. The vas deferens joins the urethra, through which they leave the body. The ureter carries urine from the kidney, so it is not involved.

Teacher's Note:
1. Ureter belongs to the excretory system.
2. Learn the path as testis, vas deferens, urethra.

Answer: (b) both (I) and (IV)

Explanation:
1. At birth the ovaries contain thousands of immature eggs, not mature eggs, so (I) is incorrect.
2. The two oviducts unite to form the uterus, an elastic bag-like structure, and not the cervix, so (IV) is incorrect.

Teacher's Note:
1. The uterus is the bag-like organ and the cervix is its narrow lower end.
2. One egg is released each month.

Answer: (c) menarche → insemination → gestation → parturition → menopause

Explanation:
1. A woman first reaches menarche, then insemination can lead to fertilisation.
2. Gestation follows, ending with parturition, and menopause comes at the end of the reproductive life.

Teacher's Note:
1. Gestation always precedes parturition.
2. Menopause is the last event.

Answer: (b) (ii) and (iv)

Explanation:
1. At puberty the rate of general body growth begins to slow down while reproductive tissues mature, so (ii) is wrong.
2. The changes take place slowly over months and years, so (iv) is wrong.

Teacher's Note:
1. Puberty brings gradual changes, and they differ in boys and girls.
2. Read each statement carefully.

Answer: (d) epididymis → vas deferens → urethra

Explanation:
1. Sperms formed in the testis first collect in the epididymis.
2. They then pass through the vas deferens and finally leave the body through the urethra.

Teacher's Note:
1. Order: testis, epididymis, vas deferens, urethra.
2. The vas deferens joins the urethra near the urinary bladder.

Answer: (b) oestrogen

Explanation:
1. Oestrogen is secreted by the ovaries.
2. With both ovaries removed, its level in the blood falls.

Teacher's Note:
1. Oxytocin and prolactin are made by the pituitary, not by the ovaries.
2. Ovaries make oestrogen and progesterone.

Answer: (a) oviduct

Explanation:
1. Tubectomy is a surgical method in women in which the oviducts (fallopian tubes) are blocked.
2. The egg then cannot reach the uterus or meet the sperm.

Teacher's Note:
1. Vasectomy blocks the vas deferens in men.
2. Tubectomy is its female counterpart.

Answer: (c) condoms

Explanation:
1. A condom is a barrier that prevents contact with infected body fluids.
2. Surgery, pills and Copper-T prevent pregnancy but do not stop the spread of infections.

Teacher's Note:
1. Only barrier methods protect against STDs.
2. Pills change the hormonal balance.

Answer: (d) syphilis

Explanation:
1. Syphilis is a bacterial disease that spreads through sexual contact.
2. The other diseases spread through insects or contaminated food and water, not sexual contact.

Teacher's Note:
1. Other STDs are gonorrhoea, warts and AIDS.
2. Syphilis is caused by a bacterium.

Answer: (c) II and IV

Explanation:
1. Genital warts and AIDS are viral diseases.
2. Syphilis and gonorrhoea are caused by bacteria.

Teacher's Note:
1. Bacterial: syphilis, gonorrhoea. Viral: warts, AIDS.
2. Antibiotics do not work against viruses.

Answer: (d) all of these

Explanation:
1. Copying DNA passes the parents' characters to the offspring.
2. Slight errors in copying give variation, which helps the species to survive over time, so all three reasons are correct.

Teacher's Note:
1. DNA copying gives both similarity and variation.
2. It is the basic event in reproduction.

Answer: (a) deoxyribonucleic acid

Explanation:
1. DNA is the genetic material of the cell present in the nucleus.
2. Its full form is deoxyribonucleic acid.

Teacher's Note:
1. DNA carries the information for making proteins.
2. Copying DNA is the basic event of reproduction.

Answer: (c) inaccuracy in the DNA copying mechanism

Explanation:
1. DNA copying is not perfectly accurate, and these small errors create variations.
2. Regeneration and fragmentation produce identical copies, not variations.

Teacher's Note:
1. Accurate copies give clones; slightly inexact copies give variation.
2. Sexual reproduction adds more.

Answer: (a) a chromosome contains hundreds of genes, which are composed of DNA

Explanation:
1. Chromosomes in the nucleus are long DNA molecules.
2. A gene is a segment of DNA and a chromosome contains hundreds of genes.

Teacher's Note:
1. Chromosome > gene > DNA stretch.
2. Genes are made of DNA.

Answer: (d) hyphae

Explanation:
1. The body of Rhizopus consists of thin thread-like tubular structures called hyphae.
2. Upright hyphae carry sporangia at their tips.

Teacher's Note:
1. Hyphae form the body of a fungus.
2. Sporangia contain the spores.

Answer: (c) A is true, but R is false.

Explanation:
1. Copper-T is an intra-uterine device that prevents pregnancy, so A is true.
2. It does not protect against sexually transmitted diseases; only a condom does, so R is false.

Teacher's Note:
1. Only barrier methods like condoms reduce the spread of STDs.
2. IUDs prevent implantation.

Answer: (c) A is true, but R is false.

Explanation:
1. Vasectomy is a surgical method of birth control done in males, so A is true.
2. It involves cutting or tying a small portion of the sperm duct (vas deferens), not the oviduct, so R is false.

Teacher's Note:
1. Vasectomy is for males and tubectomy is for females.
2. Oviduct is a female structure.

Answer: (c) A is true, but R is false.

Explanation:
1. Ovulation occurs in the middle of the cycle, around the 14th day, so fertilisation is most likely then and A is true.
2. The reason is false; the chance is high because the egg is released, not because the sperms are more active.

Teacher's Note:
1. Ovulation, not sperm activity, decides the fertile period.
2. Menstruation occurs when the egg is not fertilised.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Each month the uterus prepares to receive a fertilised egg, so A is true.
2. If there is no fertilisation, the lining breaks as menstrual flow, so R is true, but it does not explain why the lining thickens.

Teacher's Note:
1. Lining thickens to nourish the embryo.
2. It is shed when no embryo forms.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. The testes lie outside the abdomen in the scrotum, so A is true.
2. The scrotum keeps them about 2 °C cooler than the body, which sperm formation needs, so R explains A.

Teacher's Note:
1. Sperm formation needs a lower temperature.
2. The scrotum regulates the temperature.

Answer: (d) A is false, but R is true.

Explanation:
1. AIDS is caused by a virus (HIV), not a bacterium, so A is false.
2. The virus suppresses the immune system, so R is true.

Teacher's Note:
1. HIV attacks the immune system.
2. AIDS is a viral disease.

Answer: (c) A is true, but R is false.

Explanation:
1. Oral pills change the hormonal balance of the body and can cause side effects, so A is true.
2. They work by stopping the release of eggs (ovulation), not by blocking sperms, so R is false.

Teacher's Note:
1. Pills are hormonal.
2. Condoms and diaphragms block sperms.